Electric timepiece

ABSTRACT

An electric timepiece wherein a mechanical vibrator is synchronized with a signal which compares signals of a relatively high-frequency time standard with a relatively low-frequency mechanical vibrator. A first embodiment applies nonlinear characteristics of frequency in response to changes in vibrating amplitude of the mechanical vibrator. In a second embodiment, a time standard signal is utilized as a synchronizing signal to control the phase of the input signal for driving the mechanical vibrator and for synchronizing the mechanical vibrator.

United States Patent Aizawa et al.

[ 1 Mar. 14, 1972 ELECTRIC TIMEPIECE Inventors: Susanna Aizawa; KoichiNakamura; Yuki Tsuruishi, all'of Suwa-shi; Kikuo Oguchi, Suwa-gun,Nagano-ken, all of Japan Assignee: Kabmhiki Kaisha Suwa Seikosha, Tokyo,

' Japan Filed: July 16, 1969 Appl. No; 842,278

[56] References Cited UNITED STATES PATENTS 3,512,351 5/1970 Shelley etal ..58/23 3,451,210 6/1969 Helterline et a1. ..58/26 PrimaryExaminer-Richard B. Wilkinson Assistant Examiner-Edith C. SimmonsAttorney-Blum, Moscovitz, Friedman, Blum & Kaplan [57] ABSTRACT Anelectric timepiece wherein a mechanical vibrator is synchronized with asignal which compares signals of a relatively high-frequency timestandard with a relatively lowfrequency mechanical vibrator. A firstembodiment applies nonlinear characteristics of frequency in response tochanges in vibrating amplitude of the mechanical-vibrator. In a secondembodiment, a. time standard signal is utilized as a synchronizingsignal to control the phase of the input signal for driving themechanical vibrator and for synchronizing the mechanical vibrator. I

3 Claims, 15 Drawing Figures coure dLL/A/G V 5 4 pompeenva MEAVA/J/l/Gl/ FEEGUENC y 3 Z 4$CYLL4T0 wee/a 7-02 VIBE/7 7704/ M6 4! 75 4419 56 "C'OIVVEETEQ PATENTEDMAR 14 I972 3, 648,453

PATENTEDMAR 14 I972 SHEET 2 0F 6 PAIENTEUMAR 14 1972 3,648,453

sum 3 OF 6 COMPARING CICUIT PATENTEDMARMISYZ' SHEET [1F 6 mm ItPATENTEDMAR 14 I972 SHEET 8 BF 6 m m Lu 111? lall ul ELECTRIC TIMEPIECEDETAILED DESCRIPTION OF INVENTION The present invention relates to anelectric timepiece, and more particularly to an electric timepiececomprising a timekeeping oscillator and a mechanical vibrator whichdrives the gear train to operate the indicators.

A primary object of the present invention is to provide a high-precisionelectric watch which is simple in construction and cheap in price, bysynchronizing the mechanical vibrator of unstable low frequency with thetime-keeping oscillator of high frequency, without using a frequencydivider.

A further object of the invention is to provide a high-precisionwristwatch controlled by a quartz crystal.

Various types of electric watches are known wherein the balance-springoscillator of 2.5 Hz. or Hz. is used as time base. However, in thesetypes of watches it is impossible to make the daily rate within 2seconds.

A watch using, as its time base, a tuning fork which vibrates at severalhundred cycles is also known. In these watches the gear train is drivendirectly by the tuning fork. Though the daily rates of these watches arenearly 2 seconds, it is still impossible to attain a precision of 0.2second per day or better. This is because the fluctuation of the torquefor driving the gear train influences the frequency of the time-keepingoscillator, as the time-keeping oscillator and the oscillator fordriving the gear train are the same. Besides, in the tuning fork thereexists position error. And if one wants to make the daily rate less than0.2 second it is necessary to make the resonance frequency of the tuningfork over several kHz. But it is very difficult to drive the gear traindirectly by a tuning fork having such high frequency.

Quartz crystal watches having quartz oscillator of several kHz.guarantee a daily rate within 0.2 second. Quartz crystal timepiecesusually comprises quartz crystal oscillator, frequency divider, motorand gear train. The frequency divider is inevitable for dividing thefrequency of the quartz oscillator of several kHz. into the responsefrequency of the motor, i.e., several Hz. to several Hz.

This invention is particularly characterized in eliminating thefrequency divider from quartz crystal timepieces. As a result, it isapplicable to Wristwatches requiring small space and a watch of low costcan be realized. Besides, a balancespring oscillator or a synchronizedtuning fork can be used instead of motor. As these are conventionallyknown oscillators which require only small power consumption, they areeasy to manufacture it and with low cost. Thus it is very advantageousfor making a quartz crystal timepiece compact enough as a wristwatch.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a block diagram showing oneembodiment according to the present invention.

FIG. 2 is one embodiment of the block diagram in FIG. 1.

FIG. 3 is a cross-sectional view of FIG. 2.

FIGS. 4 and 5 are electric circuits of the embodiment shown in FIG. 2.

FIG. 6 is a waveform of the embodiment shown in FIG. 2.

FIG. 7 is another embodiment of the block diagram shown in FIG. 1.

FIG. 8 is a cross-sectional view of the embodiment of FIG. 7.

FIG. 9 is a tautochronous curve of the embodiment shown in FIG. 7.

FIG. 10 is a device for protecting the balance from outer disturbance.

FIG. 1 I is another embodiment of the block diagram.

FIG. 12 is a frequency-amplitude curve of the tuning fork of theembodiment shown in FIG. 1 1.

FIG. 13 shows another embodiment of the block diagram.

FIG. 14 is an embodiment using the block diagram of FIG. 13.

FIG. 15 is a waveform of the embodiment shown in FIG. 14.

FIG. 1 is a block diagram showing one embodiment of an electrictimepiece according to the present invention. I is a relatively highfrequency oscillator as the time base. 2 is a relatively low frequencymechanical vibrator, the frequency of which is l/n(n integer) of that ofsaid time keeping oscillator. 3 is means for maintaining the vibrationof the mechanical vibrator 2. 4 is means for comparing the vibratoryphase of the output from the time keeping oscillator l with that fromthe mechanical vibrator. 5 is a device which controls the frequency ofmechanical vibrator 2 to be l/n(n integer) of that of the time-keepingoscillator l. 6 is a converter which converts the vibratory motion ofthe mechanical vibrator into rotary motion to operate the indicators andthe gear train. In other words, according tothe present invention, thevibratory phase of the output from the time-keeping oscillator havingrelatively high frequency is compared directly with that from the lowfrequency mechanical vibrator, the frequency of which is as that of lowas the ordinary electric watch and l/n(n integer) of that of saidtime-keeping oscillator, and said mechanical vibrator is synchronizedwith the time-keeping oscillator.

FIG. 2 is one embodiment according to the invention wherein abalance-spring oscillator is used as the mechanical vibrator.

FIG. 3 is a cross-sectional view of said embodiment.

In FIGS. 2 and 3, 7 is a balance wheel and 8 is a hair spring. Both 7and 8 form an oscillating system. This oscillating system corresponds tothe mechanical vibrator 2 in FIG. 1. Double coil 9 comprising adetecting coil and a driving coil is fixed to the plate 10 and detectsthe variation in the magnetic flux which passes through the coil. Thatmagnetic flux is generated from the magnets 11 and 12 provided in theneutral point of the oscillation of the balance where the vibration isin static condition. As a result of the flux, the pulsive current isapplied to the driving coil. The balance is energized through theelectric circuit 13, thus the self-oscillation is maintained.

FIG. 4 is one embodiment of the electric circuit 13. 19 is a detectingcoil, 20 a driving coil. This type of electric circuit is well known inthe electric timepiece using a balance-spring as mechanical vibrator.

Self-oscillating means comprising double coil 9, magnets 11 and 12 andelectric circuit 13 in FIGS. 2 and 3 correspond to the means 3 formaintaining the oscillation in FIG. 1.

14 is a converter which converts the vibratory motion of the balanceinto rotary motion to operate the indicators. 15 is a part of the geartrain 14. I5 corresponds to the converter and gear train 6 in FIG. 1. 16is a double coil comprising a detecting coil and a control coil which isspaced by A from the neutral point of the oscillation. I7 is an electriccircuit for comparing the vibratory phase of the balance with that ofthe time-keeping oscillator. 18 is an input terminal from the timekeeping oscillator.

FIG. 5 is one embodiment of an electric circuit 17 in FIG. 2. 21 is acontrol coil, 23 is an input terminal from the time-keep ing oscillator,part A is an amplifier for the detecting signal, part B is a flip-flopwhich compares the vibratory phase of the output from the time-keepingoscillator with that from the balance. The power source is common withthat for the selfoscillating circuit shown in FIG. 4

FIG. 6 shows a waveform of each point a,b,c in FIG. 5. (i) is a waveformof point a, that is an oscillating pulse series from the time-keepingoscillator. (ii) is a waveform of point b, that is pulse series fordetecting the vibratory phase of the balance. (iii) is a waveform ofpoint c, that is the electric waveform of the control pulse, the widthof which is equal to the difference of vibratory phase between theoutput from the time-keeping oscillator and that from the balance. Thefrequency of the balance is compensated by applying the current throughthe control coil.

If the frequency of the time keeping oscillator is 2.5 kHz., the periodof the pulse series of (i) is 0.4 m.sec. And if the frequency of thebalance is 2.5 Hz., the pulse period of (ii) is 400 m.sec. As thefrequency stability of the balance-spring system is usually less than2X10, fluctuation of the pulse series is 0.08 msec. With this range, themechanical vibrator can be easily synchronized. In other words, it ispossible to divide it into l/1,000, for the frequency of the timekeeping oscillator is 2.5 kHz. and that of the balance is 2.5 Hz. So afrequency di- I vider is unnecessary.

According to Airys Theorem, the amount of compensation of the balance isnearly proportional to a/A(A z a). So if the driving pulse is appliedfar from the center of the balance, the amount of frequency compensationof the balance will become larger. The amount of frequency compensationof the balance in theory is maximum at the maximum amplitude A where thespeed of the balance is zero. On the other hand, the larger the controlpower, the larger the amount of compensation will be. And the controlpower is determined by the pulse width proportional to the phasedifference of vibration and by the peak value decided by the number ofturns of control coil 22 and the wire diameter.

Now if the peak value applied on the control coil 22 is equal to thedriving peak value applied on the self-oscillating driving coil, theratio 'r/ro(where 'r control pulse width, To driving pulse width) is theratio of control power and driving power.

Driving power is inversely proportional to the quality value of balance.The quality value is inversely proportional to the energy loss of thebalance. Therefore the amount of compensation of the balance isproportional to:

From the calculation, the proportional constant k is obtained. Thereforethe variation of the frequency of the balance The ordinary value of theelectric timepiece using the balance as the mechanical vibrator is:

Q==100 Therefore, supposing that a/A=% and 1=O.4 m.sec.(2.5kHz.):

If the peak value of control coil is twice as much as that of thedriving coil, the frequency range for synchronization is as follows:

Af/f=4Xl0 This value corresponds to 35 seconds of daily rate. With thisvalue it is easy the arrangement to a practical system.

The double coil 16, electric circuit 17 for comparing the phasedifference of the vibration and the input terminal 18 in FIG. 2correspond to the comparing means 4 and the control means 5 in FIG. 1respectively.

The magnets 11 and 12 in FIGS. 2 and 3 pass over the controlling coil inthe double coil 16 four times in one oscillation when the amplitude ofthe balance is above about 240. By selecting a triggering level of thetransitor, the detection only once in one oscillation can be easilygained. We name the control system shown in FIGS. 2 and 3 thephase-controlling system.

FIG. 7 is the other embodiment according to the invention wherein abalance-spring oscillator is used as a mechanical oscillator.

FIG. 8 is a sectional view of FIG. 7.

The difference from FIG. 2 is that the detecting coil for controllingand that for self-oscillation are the same, and that the control pulseis added at the neutral point of the balance where vibration is instatic condition.

Generally, by adding the power at the neutral point of the oscillation,energy can be given to the balance to change the amplitude withoutcausing variation in the frequency.

In contrast with this, adding the power to the balance at the maximumamplitude, the variation of the frequency is largest but energy cannotbe given to the balance.

Therefore the coil 24 is a triple one and the detecting coils areincluded both in the self-oscillating electric circuit 25 and in theelectric circuit 26 for comparing the phase of vibration.

An iron piece 27 is secured to a member made of Bakelite having weakmagnetic permeability and also weak specific electric conductivity atthe opposite position to the neutral point of oscillation. As a result,the tautochronism shows the characteristic as shown in FIG. 9 such thatthe watches lose abruptly if the amplitude of the balance increases. Asthe magnets 29,30 and the iron piece 27 act with each other at anamplitude of about I", the tautochronous curve as shown in FIG. 9 can beobtained.

In order to explain this control system it is supposed that in FIG. 9,the frequency of l/n(n:integer) of the time keeping oscillator equals tothat shown by the dotted line crossing a point Q and further the pulsewidth of control as shown in FIG. 6 (iii) equals just a half of theperiod of the time-keeping oscillator pulse and under this condition theamplitude of the balance is just 207.

Now, if the watch loses due to disturbance, as can be seen in FIG. 6,the detecting pulse (ii) generates later and so the controlling pulse(iii) becomes smaller than in the steady state mentioned before.Therefore the energy to be added to the balance decreases and theamplitude of the balance becomes small. Then as can be seen from thetautochronous curve in FIG. 9, the operating point moves from the pointO to Q and the watch gain abruptly till the next detecting pulse (ii)generates and try to recover its time delay.

If the loss to be recovered is smaller than that due to disturbance, thewidth of the next control pulse is smaller than that in steady state butlarger than this one. Therefore the operating point moves to the point 0between 0 and 0,, the watch gains further till the next detecting pulse(ii) generates and try to recover its time delay.

On the other hand, if the loss to be recovered is larger than that dueto the disturbance, the watch gains and the width of the next controlpulse is larger than that in the steady state and the energy to be addedto the balance increases more than that in the steady state and theamplitude of the balance also increases. Now the operating point movesto the point 0 and the watch loses till the next detecting pulse (ii)generates and try to make the difference from the standard equal tozero.

Repeating the above-mentioned operations, the operating point travels tothe point Q and finally settles there. If the watch gains due to thedisturbance, the operating point also settles on the point Q finally.

The frequency of the balance is synchronized with that of the timekeeping oscillator by maintaining the operating point 0 againstdisturbance and controlling the amplitude constant, at about 207. Inthis case, the efficiency of the control depends on the product of thegradient of the tautochronous curve and the control power. According tothe result of an experiment, the frequency range of synchronization ofabout 30 seconds in daily rate could be obtained by using a time keeping oscillator of 2 kHz. Therefore it is understood that this system iseasy for application.

The characteristic of this system is to control the frequency of thebalance at l/n(n: integer) of that of a time keeping oscillator bygiving a nonlinear characteristic to the balance and keeping theoscillation of the balance always constant. We name thisAmplitude-controlling system."

Since the frequency of the balance shown in the above description as anexample of the mechanical vibrator is extremely low compared with othermechanical vibrators wristwatches using the balance are apt to undergodisturbance.

In FIG. 10, in order to eliminate the influence of disturbance, twobalances shaped into wheels form in their outer peripheries engage eachother. As the rotary direction of the two balances is the same for thedisturbance, if the moment of inertia and gear ratio of the two balancesare properly selected respectively, the influence of disturbance isabsorbed by each other. In this manner, the condition that there is nodisturbance can be produced. Therefore concerning the balance, it is notnecessary to pay attention to a large shift of phase owing to somedisturbance shocks. A tuning fork having a frequency of several hundredHz. may be used as a mechanical vibrator 2 in FIG. 1.

FIG. 11 shows the amplitude-controlling system applied to a tuning fork.This control device comprises the tuning fork 31, magnets 32,33 fixed tosaid tuning fork, coils 34,35 which act with said magnets, electriccircuit 36 for self-oscillation of the tuning fork in which the voltageof the detecting coil forming a part of coil 34 is used as the input andthe coil 35 is used as a driving coil, and electric circuit 38 forcontrolling the tuning fork by supplying an electric current to thecontrolling coil forming a part of coil 34 comparing the input 37 from atimekeeping oscillator with that from said detecting coil. In this case,the frequency of the tuning fork is also synchronized with atime-keeping oscillator in the same manner as the balance. The tuningfork has a nonlinear characteristic owing to the action of the othermagnet 39 fixed to said tuning fork and the iron piece 40 secured on thebaseplate.

FIG. 12 shows said nonlinearcharacteristic, and and a solid line beingthe tautochronous curve. A mixed line shows the frequency-amplitudecurve of the tuning fork exciting. A dotted line shows the frequency of1/n(n: integer) of that of a time-keeping oscillator. Owing to the sameoperation as in the case of the balance, the amplitude of the tuningfork is kept constant. The magnet 39 may be used with the magnet 32 orthe magnet 33. The process that the oscillation of the tuning fork istransmitted to the gear train and the indicators through the click 41and the ratchet wheel 42 is exactly the same as conventional tuning forkwatches. A converter such as a magnetic escapement may be used. When thetuning fork is used as a mechanical vibrator, the followingcharacteristics can be found. First, there is no influence ofdisturbance, for the frequency of the tuning fork is about 400 Hz.Second, the mechanical vibrator can be easily controlled, for thedividing ratio of the frequency of the tuning fork and a time-keepingoscillator having the frequency of several kiloHertz becomes small.

FIG. 13 shows a block diagram of the other examples according to thepresent invention. The difference from FIG. 1 is that the comparingmeans, the operating means for self oscillations and the controllingmeans are united as shown 45. 43 is a time keeping oscillator. 44 is amechanical vibrator having the frequency of l/n(n: integer) of that of atime-keeping oscillator 43. 46 is a converter and gear train throughwhich the vibration of the mechanical vibrator 44 is transmitted to theindicators.

FIG. 14 shows one embodiment of FIG. 13. The voltage induced in adetecting and driving coil which interacts with the magnet 48 fixed onthe tuning fork 47 is fed back to the base 52 of transistor 51 throughthe transformer 50. As the signal from a time-keeping oscillator hasbeen added to the base 52 from the terminal 53, when the sum of saidvoltage and said signal attains the trigger level, the transistor isswitched on and the current is applied to the coil 49. When the currentbegins to flow, it is applied increasingly owing to the feedback of thetransformer 50 during the time of pulse width decided from the electriccircuit.

FIG. (1) shows the induced voltage wave form of the coil 49. Actually atdriving the waveform is varied by the driving current, but for easierunderstanding the waveform at nondriving is shown here. This is notessential for the explanation of this phenomenon. The same may be saidof (iii). Next (ii) is a signal from a time keeping oscillator. (iii) isa base waveform of the tuning fork at nondriving, which is the sum of(i) and (ii). Taking the trigger level on the position shown by themixed line, the driving waveform is as shown in (IV). The pulse width 1is not changed as before mentioned, but it can be seen that thedeviation between the neutral point of oscillation and that of thedriving pulse changes according to the difference between the phase ofvibration of the tuning fork and that of the time-keeping oscillator.The energy to be added to the tuning fork is changed according to thephase of the tuning fork when the driving pulse is added. Theinteraction between the magnet 54 secured on the tuning fork and theiron piece 55 fixed to the baseplate shown in FIG. 14 can give anonlinear characteristic as shown in FIG. 12 to the tuning fork. So thefrequency of the tuning fork can be controlled to be 1 /n(n integer) ofthat of a time-keeping oscillator by keeping the amplitude constant,cooperating with the energy change before'mentioned.

The characteristic according to this method is to unite the comparingmeans, self-oscillating driving means and control means and to make thewhole composition very simple. According to the results of anexperiment, when the crystal oscillator of 16 kHz. is used as atime-keeping oscillator and the tuning fork of 400 Hz. is used as amechanical vibrator, the frequency range of synchronization, 7X l 0Hz.corresponding to about 1 minute of daily rate could be obtained.

According to the present invention, a mechanical vibrator having arelatively low frequency such as the balance and the tuning fork etc.,can be controlled directly by a time-keeping oscillator having arelatively high frequency such as a crystal oscillator of severalkiloHertz. Thus it is not necessary to provide a divider. In thismanner, we can obtain electric watches having simple constructions withlow cost. Further the production of high-precision watches has been madepossible by the adoption of a high frequency time-keeping oscillator.For a high frequency time-keeping oscillator has a high accuracy ingeneral, for example, the daily rate of 0.2 second can be obtained bythe crystal oscillator of several kiloHertz.

What is claimed is:

1. An electric timepiece comprising a time standard oscillator having arelatively high frequency, a mechanical vibrator having a frequency ofabout l/n(n=an integer) of said time standard oscillator; means forsustaining the oscillation of said mechanical vibrator; an indexingmechanism; means for transmitting the oscillation of said mechanicalvibrator to said indexing mechanism; means for directly comparing thephase of said time standard oscillator with that of said mechanicalvibrator to produce an output signal proportional to the differencetherebetween; control means for controlling the frequency or the phaseof said mechanical vibrator in response to said output signal of saidcomparing means for sustaining the frequency of said mechanical vibratorat 1/n of the frequency of said time standard oscillator, said controlmeans being adapted so that the magnitude of the input energy suppliedto said mechanical vibrator is changed in response to said outputsignal; and permanent magnet means positioned adjacent said mechanicalvibrator for cooperation therewith to cause the changes in the frequencyof said mechanical vibrator in response to vibration amplitude changesto follow a nonlinear characteristic.

2. An electric timepiece comprising a time standard oscillator having arelatively high frequency including a quartz crystal vibrator, a tuningfork-type vibrator having a frequency of about l/n(n=an integer) of saidtime standard oscillator; electromagnetic means for sustaining theoscillation of said mechanical tuning-fork-type vibrator; an indexingmechanism; means for transmitting the oscillation of saidtuning-fork-type vibrator to said indexing mechanism; means for directlycomparing the phase of said time'standard oscillator with that of saidtuning-fork-type vibrator to produce an output signal proportional tothe difference therebetween; and control means for controlling thefrequency or the phase of said tuning-fork-type vibrator in response tosaid output signal of said comparing means for sustaining the frequencyof said tuning fork type vibrator at l/n of the frequency of said timestandard oscillator, said control means being adapted so that the phaseor magnitude of the input energy supplied to said tuning-fork-typevibrator is changed in response to said output signal and permanentmagnet means positioned adjacent said tuning fork vibrator forcooperation therewith to cause the mechanical vibrator in response tosaid output signal of said comparing means for sustaining the frequencyof said mechanical vibrator at l/n of the frequency of said timestandard oscillator, said control means being adapted so that the phaseor magnitude of the input energy supplied to said mechanical vibrator ischanged in response to said output signal.

1. An electric timepiece comprising a time standard oscillator having arelatively high freQuency, a mechanical vibrator having a frequency ofabout 1/n(n an integer) of said time standard oscillator; means forsustaining the oscillation of said mechanical vibrator; an indexingmechanism; means for transmitting the oscillation of said mechanicalvibrator to said indexing mechanism; means for directly comparing thephase of said time standard oscillator with that of said mechanicalvibrator to produce an output signal proportional to the differencetherebetween; control means for controlling the frequency or the phaseof said mechanical vibrator in response to said output signal of saidcomparing means for sustaining the frequency of said mechanical vibratorat 1/n of the frequency of said time standard oscillator, said controlmeans being adapted so that the magnitude of the input energy suppliedto said mechanical vibrator is changed in response to said outputsignal; and permanent magnet means positioned adjacent said mechanicalvibrator for cooperation therewith to cause the changes in the frequencyof said mechanical vibrator in response to vibration amplitude changesto follow a nonlinear characteristic.
 2. An electric timepiececomprising a time standard oscillator having a relatively high frequencyincluding a quartz crystal vibrator, a tuning fork-type vibrator havinga frequency of about 1/n(n an integer) of said time standard oscillator;electromagnetic means for sustaining the oscillation of said mechanicaltuning-fork-type vibrator; an indexing mechanism; means for transmittingthe oscillation of said tuning-fork-type vibrator to said indexingmechanism; means for directly comparing the phase of said time standardoscillator with that of said tuning-fork-type vibrator to produce anoutput signal proportional to the difference therebetween; and controlmeans for controlling the frequency or the phase of saidtuning-fork-type vibrator in response to said output signal of saidcomparing means for sustaining the frequency of said tuning fork typevibrator at 1/n of the frequency of said time standard oscillator, saidcontrol means being adapted so that the phase or magnitude of the inputenergy supplied to said tuning-fork-type vibrator is changed in responseto said output signal and permanent magnet means positioned adjacentsaid tuning fork vibrator for cooperation therewith to cause the changesin the frequency of said tuning fork vibrator in response to vibrationamplitude changes to follow a nonlinear characteristic.
 3. An electrictimepiece comprising a time standard oscillator having a relatively highfrequency, a mechanical vibrator having a frequency of about 1/n(n aninteger) of said time standard oscillator, said mechanical vibratorhaving two balance wheels operatively coupled to each other and mountedfor rotation in opposed directions whereby said vibrator is unaffectedby external shock; means for sustaining the oscillation of saidmechanical vibrator; an indexing mechanism; means for transmitting theoscillation of said mechanical vibrator to said indexing mechanism;means for directly comparing the phase of said time standard oscillatorwith that of said mechanical vibrator to produce an output signalproportional to the difference therebetween; and control means forcontrolling the frequency or the phase of said mechanical vibrator inresponse to said output signal of said comparing means for sustainingthe frequency of said mechanical vibrator at 1/n of the frequency ofsaid time standard oscillator, said control means being adapted so thatthe phase or magnitude of the input energy supplied to said mechanicalvibrator is changed in response to said output signal.